Heart failure affects approximately 5 million people in the United States. Many moderate to severe heart failure patients may also have a condition in which the two lower chambers of the heart (known as the left and right ventricles) are not beating together as they do normally. In medical terms, this condition is called “ventricular dysynchrony.” Ventricular dysynchrony disturbs the synchronous beating of the heart, and as a result the heart does not pump blood adequately to meet the needs of the body. More specifically, ventricular dysynchrony typically results from intraventricular conduction delays (IVCD) that disturb the synchronous beating of the ventricles. Typically, the IVCD has a left bundle branch block (LBBB) morphology.
One previous method for optimizing cardiac pacing for intra-left ventricular resynchronization involves modifying pacing to reduce QRS duration. Even though QRS duration can be reduced, reduction in QRS duration does not guarantee optimal hemodynamic cardiac operation. Kass et al., Improved left ventricular mechanics from acute VDD pacing in patients with dilated cardiomyopathy and ventricular conduction delay, Circulation 1999; 99:1567–73.
Another previous method for optimizing cardiac pacing for intra-left ventricular resynchronization involves modifying pacing to improve cardiac ventricle filling. Typically cardiac ventricle filling is measured by echocardiography. Although cardiac filling is one aspect of hemodynamics, tests have shown that optimal hemodynamic cardiac operation by pacing does not result from better cardiac filling. Auricchio et al., Cardiac resynchronization therapy restores optimal atrioventricular mechanical timing in heart failure patients with ventricular conduction delay, J. Am Coll Cardiol 2002; 39:1163–9.
One therapy to treat left ventricle dysynchrony is Cardiac Resynchronization Therapy (CRT). CRT is a new, proven treatment for selected patients with heart failure-induced conduction disturbances and ventricular dysynchrony. When used in combination with stable, optimal medical therapy, CRT is designed to reduce symptoms by restoring the mechanical sequence of ventricular activation. Cardiac resynchronization therapy (CRT) provides atrial-synchronized, biventricular pacing using standard pacing technology combined with a special third lead which is implanted via the coronary sinus and positioned in a cardiac vein to sense and pace the left ventricle. Following a sensed atrial contraction, both ventricles are stimulated to contract more synchronous. The resulting resynchronization of ventricular contraction reduces mitral regurgitation and optimizes left ventricular filling, thereby improving cardiac function.